Have good quality video 720p in 16:9 framingHave good commentary with your microphone, use audacity cause with that you can kill room noise.If you want to do the whole facecam thing, make sure that is good quality as well.

I never really understood the attraction with the whole "let's play" phenomenum. I much prefer watching speedruns, which I guess in a way is a type of let's play, but from my point of view there has to be something extraordinary about either the way you play the game, for it to be worth my time.

Humour! Humour is a great way to enhance your LP! For one, it contrasts against the darkness of the game itself thus making the videos more enjoyable to watch rather than just pure walkthrough-style blankness, while at the same time emphasising how scary the game is in the first place. It also makes the play-through seem more personal, like you yourself are doing it and not just some mindless robot programmed to play video games. For viewers with a lower horror tolerance, it will soften the experience and broaden your target audience.

Good quality recording is also essential, like SalvatoreHaran said. That means video and audio! Nothing is more annoying than terrible audio quality from the commentator. Make sure the balance is right - we should be able to hear the game as though we're playing it and hear you like you're sitting next to us in the same room.

I personally like it when LP'ers commentate on how the game compares to other horror games - how does it compare to the Silent Hill franchise (the awesome games rather than the...less-awesome installments) or the Amnesia games or the Resident Evil games or the Penumbra games? Even better when it's compared to books and films. I flail happily whenever Lovecraft is mentioned, but that's mostly because I'm a huge Lovecraft fangirl.